The present invention relates to an automatic clearance adjusting mechanism in a brake including means for preventing a so-called drag or residual friction phenomenon.
A number of mechanisms for automatically adjusting increase of the brake clearance between a rotor member and a friction pad due to wearing of the friction pad of a brake are known. One known type of clearance adjusting mechanism provides that the piston is retained by the actuator by virtue of friction, while being allowed a certain preset amount of axial sliding. In an example of this type an iron ring is mounted in the middle part of the cylinder with a certain fixed amount of axial play. The piston can advance against the friction force with the iron ring in response to the wear of the friction pad. In another example, a seal concurrently functions as a friction ring.
As the abovementioned type of automatic clearance adjusting mechanism can be so simply assembled that it now enjoys a widespread application, it is accompanied by, however, a serious disadvantage that a so-called drag readily takes place in it. That is to say, when an extremely high hydraulic brake pressure is applied a large elasticity deflection takes place in the brake component elements, resulting in occurrence of the relative displacement surpassing the elasticity deflection capacity of the seal between the piston and the cylinder, accompanied by a sliding between the seal and the piston.
As a result of it the seal which is to impart the restoring force to the piston loses the ability of restoring it even after the hydraulic pressure has been released; moreover the same may sometimes work in a manner, on the contrary, to push out the piston. Once this situation has been set the friction pad is urged against the rotor member with a certain pressure (this phenomenon is named the so-called drag phenomenon), which not only brings about power loss but also may develop into more serious dangers such as overheating of the brake, abnormal wearing of the lining, vapor lock, etc.
In order to evade this danger rendering the brake clearance surpassing the elasticity deflection of the brake component elements is enough, which is, however, impracticable in fact because of increasing the amount of oil used with the result of considerable increase of the brake travel. Various propositions on the mechanism of preventing the drag phenomenon have been made. No techniques capable of solving this problem including two contradictory requirements, i.e. reduction of volume of oil used and prevention of drag phenomenon have been known to date.